pergola concrete base

v1rtu0s1ty(5a)July 6, 2010

Good afternoon folks. I would like to add a pergola to my garden. I couldn't decide how I would put the vertical wood to the ground. My neighbor built a deck and he put an 8 inch diameter concrete tube and put cement. After the concrete hardened, he just put the 6x6 on top of the concrete tube.

I was thinking of doing the same. I am thinking of building about 15 ft x 11 ft pergola. I am worried that if I put the foundation wood on the hole, it might rot eventually.

How is it properly done?

Thanks!

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marcinde(7)

Are you stick-building it (from scratch) or using a kit? It makes a difference because of how you plan to keep the structure from racking or shifting after it's built.

I generally dig a footer to frost depth, put in 8" of concrete, set my post, do another 8" of concrete around the post, backfill, and go from there. Yes it's in contact with the ground, but it's sturdy as heck.

    Bookmark   July 6, 2010 at 10:22PM
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v1rtu0s1ty(5a)

Hi marcinde. I'll be buying the materials from Home Depot so it's not going to be a kit.

Oh, here in our area, we are required to dig a least 4 ft deep since frost goes upto 3 ft. That's what they said.

So using the metal clamp screwed to the concrete base isn't good? What do you think about rotting? But yours will really be that sturdy!

    Bookmark   July 6, 2010 at 11:53PM
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rosiew(8 GA)

bumping - and I'd like to hear more about this.

    Bookmark   July 19, 2010 at 8:58PM
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marcinde(7)

Ok, so what you're talking about is a post-base connector, and it usually bolts onto an L-shaped threaded rod set in the concrete. It'll work, but you're still going to have to resist the sideways forces. You can do this with diagonal bracing, which works- it's just more of a challenge to integrate it into the design. Also, in this way, it's the wood and the fasteners giving the structure its rigidity. Which is cool, but wood (especially pressure-treated, and especially p/t from the big box stores) is going to move on you, and potentially loosen the connections over time. We just replaced a wood pergola for a client where this happened in a big way.

As for rot, yes, wood in direct ground contact is going to rot at some point. It's worth asking the question, how many years of service do you hope to get from this structure? If you're planning on a long service life you may want to explore other options for your posts, like structural fiberglass, etc. I'm giving a manufacturer of fiberglass pergola kits a try right now, and I'm pretty stoked about what they've sent.

    Bookmark   July 21, 2010 at 1:25PM
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woodyoak zone 5 Canada

marcinde - is there a link to the product you're trying? I'd be interested in seeing what they have....

    Bookmark   July 21, 2010 at 4:14PM
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marcinde(7)

The company is called Arbors Direct; they come up in Google. The reason I mention it for this application is that the way it gets its strength is the posts are hollow, with a threaded rod inside. You torque it down so everything is locked together in tight compression, preventing movement. What was kind of cool is they'll paint it in any Sherwin-Williams or Benjamin Moore color, so the homeowner and I sat out there with my fan deck and got it to match the trim color on the house pretty well.

They're not cheap, but you're essentially getting a kit that you just have to put together. No instructions, though. Picture a challenging piece of furniture from IKEA and you're on the right track.

    Bookmark   July 21, 2010 at 5:32PM
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